Sally ⇒
4 hours = 1 room
1 hour = 1/4 of the room
Steve ⇒
9 hours = 1 room
1 hour = 1/9 of the room
Sally + Steve ⇒
1 hour = 1/4 + 1/9 = 9/36 + 4/36 = 13/36
Number of hours needed ⇒
1 ÷ 13/36 = 1 x 36/13 = 36/13 = 2 10/13 hours
Answer: They need 2 10/13 hours.
